Overhead doors such as rolling metal doors and metal and fabric curtains are commonly counterbalanced by torsion spring assemblies which include a support shaft which extends through the torsion spring. Conventionally, the support shaft is anchored at one end to a non-movable support mounted to the building structure to which one end of the spring is also mounted. The opposite end of the support shaft is mounted to a second non-movable support also mounted to the building structure.
The opposite end of the torsion spring is anchored, for example, by a cup-like socket or retainer often referred to as a winding cone, which is retentively secured at a fixed support shaft location. The winding cone is used as an adjuster for varying the tension of the torsion spring. With the door in a closed position selected tension is imparted to the spring. This tension is transmitted by, for example, cables connecting the shaft to the door, to counterbalance or compensate for the weight of the door.
Typically, a torsion spring is fabricated with no gaps or spaces between its coils when the spring is in a free or untensioned state. As turns are applied to a spring the number of active coils increases. As the number of active coils increases the length of the spring also increases. In assembling the torsion spring assembly on a door the ends of the spring are securely connected to the anchors while simultaneously stretching the spring to space its coils apart. Coil spacing is required to allow space for additional coils to be formed later as the spring is twisted to perform its counterbalancing function.
As spring tension is applied during door operation the physical properties of the spring material may be adversely affected, thereby increasing the risks of premature spring breakage. “Snake-like” or serpentine appearance of the tensioned spring from improper pre-stretch or tensioning is particularly problematic in causing premature torsion spring failure.
Accordingly, there is still a continuing need for improved overhead door torsion spring tension system designs. The present invention fulfills this need and further provides related advantages.